The phenotypic and genetic effects of drought-induced stress on apical growth, ring width, wood density and biomass in white spruce seedlings

Forest plantations play an important role in maintaining a supply of high-quality timber from managed forest. With an expected increase in the prevalence of drought in some forested areas, climate change increases concerns about future seedling growth. A promising approach to promote the suitability of plantation seedlings to current and future climate would be to use variation in growth and wood traits of trees under drought as selection criteria in tree breeding programs, especially at a young stage when they are most vulnerable to drought. We evaluated the genetic control of the growth and wood density response of white spruce clonal seedlings submitted to various drought conditions in a greenhouse experiment. By varying the watering treatment of 600 two year-old seedlings from 25 clones, we simulated three levels of drought-induced stress during two growing seasons. Apical and radial growth decreased markedly as the intensity of drought increased, whereas wood density tended to increase. We also developed a woody biomass index composed of wood density and ring area, which was observed to decrease slightly with increasing drought. There was important variation in all traits among clones and heritability tended to decrease with the intensity and duration of drought-induced stress, mainly for wood density and radial growth. However, the heritability of apical growth tended to increase under drought conditions. Our results show that the response of young white spruce clones to drought is highly variable, and together with the significant levels of heritability noted, the results indicate that multi-trait genetic selection for drought stress response at a young age could represent a promising approach to increase resilience to drought.